12.2 Adding a Logger Tag to Record Data for the Booster Tank Level
Any tag that has a numeric value can have its live data plotted on the Historical Data Viewer page. Live data is data that is being read instantly from the equipment in your physical system.
You can also plot historical data on the Historical Data Viewer page however, to do so your application must include a logger tag for each tag for which you wish to plot historical data. A logger tag handles the logging or recording of tag data to disk.
By default, the data files created by logger tags are given the tag's name, followed by the extension ".DAT".
A logger tag can reco5rd values from any tag whose value is numeric. Referring to the system plan, the client has identified the need for a record of the changing levels of the booster tank over time. In the Tag Table (see Create a Tag Table), it was noted that we require a logger tag named "Log20_1" to monitor the values of "AI20_1 Booster Tank Level".
According to the client's as specified in the system plan, the data for "AI20_1 Booster Tank Level" must be recorded every six seconds. To create a new logger tag to record data for "AI20_1 Booster Tank Level", follow the directions below.
1. Click the Configure button to open the Configuration Toolbox.
2. Click the Tag Browser button in the Configuration Toolbox. The Tag Browser opens.
3. Select Logger from the Types drop-down list. Because no logger tags have been created so far, the tag list is empty.
4. Click the New button. A new logger tag properties folder opens, displaying the ID tab and its properties.
5. Enter "Log20_1" in the Name field (as per our system plan).
6. Select "Tank" from the Area field's drop-down list.
7. Enter "Log Booster Tank Level" in the Description field. The completed ID tab should appear similar to the one displayed below.
8. Click the Conditions tab to open it.
9. Click the tag browser button. The Tag Browser opens and displays all the available tags with numeric values.
10. Select the "AI20_1 Booster Tank Level" tag from the tag list.
11. Ensure that "1" is entered in the Enable field. This enables the logger tag (i.e. switches the logger tag "on") and will cause it to begin recording data once the configuration of the logger tag is complete. The completed Conditions tab should appear similar to Figure 159.
Figure 159
12. Click the Log Rate tab to open it.
13. Enter "6" into the Interval field. This sets the data for "AI20_1 Booster Tank Level" to be recorded every 6 seconds (as per the client's request).
14. Enter "10000" in the Number Of Records In File field.
This sets the data file to record a maximum of 10,000 records before the data gets bumped and new data is recorded over it.
15. Select the Create File Full Size checkbox.
16. Enter "10" in the Number Of Records In RAM field.
This sets the logger to buffer 10 records in memory before writing them to the data file. If this field is set to a large number, data can easily be lost in the event of a power failure or other error. The completed Log Rate tab should appear like the one shown below.
By setting the Interval to "6" and the Number Of Records In RAM to "10", you've configured the logger will write data to disk every 60 seconds. It is recommended that you do not set this time span any higher than one minute, you run the risk of substantial data loss in the event that the system should experience a failure.
17. Click the OK button. The new logger tag is added to the Tag Browser.
18. Close the Tag Browser.
19. Close the Configuration Toolbox.
Because you are using the tutorial simulator to supply data for the application, it is always "online". The logger tag will immediately begin to log data for the "AI20_1 Booster Tank Level" tag.
If you open your application directory, you will see that VTS has automatically generated a data file ("AI20_1.DAT") and a log file ("AI20_1.LOG"). The data file is storing the recorded data from the tag, while the log file is keeping track of the data files applicable to this tag.
Although the logger tag is now actively logging data, before you can view this file data on the Historical Data Viewer page, we must first configure a pen to plot it. This will be the task of the next exercise.